Field of the Invention
The invention relates to a device for controlling an in-cylinder pressure sensor integrated with a glow plug.
Background Art
An in-cylinder pressure sensor integrated with a glow plug for detecting the pressure in a combustion chamber of an internal combustion engine is well known, which has a pressure receiving portion constituted by a heater of a glow plug incorporating a heat generating element. Japanese Patent Laid-Open No. 2009-222031 for example discloses, as a device for use with such an in-cylinder pressure sensor, a device that estimates the amount of deposit accumulated between a cylinder head and a pressure receiving portion in an internal combustion engine when the internal combustion engine is in a predetermined operating condition, and that energizes a heat generating element on the basis of the estimated amount of deposit. In this device, the amount of deposit is estimated on the basis of the amount of heat generated in the combustion chamber, the waveform of a signal from the in-cylinder sensor and the surface temperature of the heater.
When the amount of deposit accumulated between the cylinder bead and the pressure receiving portion is increased, there arises a problem of increase in sliding friction of the pressure receiving portion, which reduces the detection accuracy of the in-cylinder pressure sensor. The above-described device can energize the heat generating element on the basis of the estimated amount of deposit and can therefore decompose and remove any deposit accumulated between the cylinder head and the pressure receiving portion by increasing the temperature of the heater at a suitable time on the basis of the estimated amount of deposit.
Energization of the heat generating element is accompanied by consumption of electric power. It is, therefore, undesirable to frequently energize the heat generating element, even though the energization is performed for the purpose of decomposing and removing the accumulated deposit. In the art disclosed in Japanese Patent Laid-Open No. 2009-222031, the amount of accumulated deposit is indirectly estimated by using, for example, the amount of heat generated in the combustion chamber and the waveform of the signal from the in-cylinder pressure sensor for the amount of deposit, and the estimation accuracy is not always correct. There is therefore, a possibility of unnecessary energization of the heat generating element.